This invention relates to a method for the time-correction of a digital switching signal which can occur only at discrete times as a consequence of the scanning process by which the digital signal to be switched is derived and which is therefore delayed relative to its desired time of occurrence.
In television technology switching signals are frequently used which serve to switch from one picture signal source to another within the visible picture. These switching signals are formed in the case of analog technology by passing line or image frequency pulses (for example saw-tooth, triangular or parabolic waveforms), or video signals originating from any desired picture signal source, via a threshold value circuit which generates a switching signal when the applied signal exceeds the threshold value.
However, in digital video technology, which is based upon scanning at discrete times, the exceeding of the threshold value can only be ascertained when the next scanned value of the digital signal is available. Thus if a switching signal is used which is formed by a simple comparator as in analog technology, the signal will in general be delayed relative to the point in time at which the original analog signal would have exceeded the threshold value. This can lead to disturbing saw-tooth structures in the reproduced picture with edges running slighting inclined from the vertical. It is the intention of the present invention to avoid or reduce these faults.